• Many plants are known to contain biologically active chemicals like digitoxin, colchicines and atropine which can treat a variety of human and animal diseases. On the same note a number of plants contain constituents which produce an adverse effect on human and animals. In Pennsylvania the economic loss due to ingestion of poisonous plants especially by livestock is relatively less compared to other states. Different groups of poisonous plants exist in Pennsylvania.
  
  

Sweet Clover

• Ingestion of sweet clover causes hemorrhaging in cattle and the severity of the disease is dependent on the age of the animal. Sweet clover is poisonous due to the formation of dicoumarin in hay. The symptoms of the poisoning occur as nose bleeds and doughy swellings on the abdomen and legs from the rapid collection of blood. There is a stiffness of joints due to internal hemorrhaging of the joints and muscles. Blood loses the capacity to clot.
  
  

Algae

• Certain fresh water algae are extremely poisonous for all species and causes a rapid and fatal poisoning upon ingestion. This is very common during hot weather and drought when the algae concentrates in the stagnant water. Due to the shortage of water animals are driven to the water. The symptoms of the poisoning are similar to those of cyanide poisoning. If the animals do survive they develop severe photosensitization. Cyanide poisoning effects the body by eliminating its ability to utilize oxygen. Photosensitization is a condition in which the liver is not able to excrete the metabolite of chlorophyll from the ingested plants. This starts to accumulate in the skin and causes the skin to burn when exposed to sunlight.
  
  

White Snake Root

• White snake root resembles the ageratum in flower and foliage but is taller and the white flower heads are looser. The plant is found in Pennsylvania but cattle eat it only when there is nothing else available. The symptoms of the poisoning cause weakness and trembles. Animals refuse to eat and crouch with half-closed eyes. In cattle the poison is carried out through the milk and causes poisoning in calves and human. The poisoning in humans is referred to as milk sickness. There were a number of cases of milk sickness reported in humans during the early 20th century.